Semiconductor integrated circuit (IC) technology is continually progressing to circuit layouts having smaller feature sizes as well as increased density. As a result of this continuous progression, photolithography systems are utilizing shorter wavelength light such as extreme ultraviolet (EUV) in order for enhanced resolution. These enhanced resolution systems typically require a high power optical source. High power optical sources may cause some reactions on the lens of the lithography system and can introduce various defects including particles, contaminations, and other types of damage.
It is desired, therefore, to provide a method and apparatus for monitoring lens contamination. It is also desired that the method and/or apparatus be cost effective.